Bad news for the Vikings on Tuesday as their top free agent acquisition entering the 2012 season left practice with a sprained medial collateral ligament in his knee. The good news is the injury won't require surgery, and Carlson should be ready for the regular season opener September 9th against the Jacksonville Jaguars.

"You dont' have to have any surgery," head coach Leslie Frazier said. "It heals by itself."

Carlson, a Litchfield, Minnesota native, missed all of last season because of a shoulder injury. He signed a five-year, $25 million contract in March.